A region neighborhood graph can be constructed from a

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Unformatted text preview: . A region neighborhood graph can be constructed from a quadtree image representation, from run length encoded image data etc. Very often, the relative position of two regions ca be used in the description process- for example, a region A may be positioned to the left of a region B, or above B, or close to B, or a region C may lie between regions A and B, etc. we know the meaning of all of the given relations if A, B, C are points, but, with the exception of the relation to be close, they can become ambiguous if A, B, C are regions. For instance, the relation to the left of can be defined in many different ways: All pixels of A must be positioned to the left of all pixels of B At least one pixel of A must be positioned to the left of some pixel of B The center of gravity of A must be to the left of the center of gravity of B. All these definitions seem to be satisfactory in many cases, but they can sometimes be unacceptable because they do not meet the usual meaning of being to the left of. Human observers are generally satisfied with the definition: The center of gravity of A must be positioned to the left of the leftmost point of B and (logical AND) the rightmost pixel of A must be left of the rightmost pixel of B [P.H Winston, The psychology of Computer Vision, McGraw Hill, NY, 1975]] Summary shape representation and description: Shape representation and description • Region description generates a numeric feature vector or a non-numeric syntactic description word, which characterize properties of the described region • While many practical shape description methods exist, there is no generally accepted methodology of shape description. Further, it is known what is important in shape. • Shape may change substantially with image resolution. Conventional shape descriptions change discontinuously with changes in resolution. A scale space approach aims to obtain continuous shape descriptions for continuous resolution changes. • The shape classes represent the generic shapes of the objects belonging to the s...
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